This is where you may need the most help, and there are many sources available. Manufacturers often have good advice but it is the effective combination of different products which is the key to good work. "God is in the details" ... and the weather threatens to get through them too.

Pre-planning to fit everything together neatly and effectively is part of an architect's job.

What materials you will use and the way your building will be constructed are fundamental decisions and costly - even sometimes illegal - to get wrong.

Your Local Authority - the Council - will want to know and approve the work before it starts, which usually means providing technical drawings. They may also want to check for fire safety with the Fire Brigade and ask for calculations to prove the structural work is up to standard.

Ensure you respect the environment when you specify materials: • use timber from properly managed forests • avoid materials which cannot be recycled • avoid materials which give off noxious gases or fibres • try to select the least energy intensive materials in production and delivery (this is hard to track, do your best!) • select materials with recycled sources, eg glassfibre insulation can now be entirely from old bottles • select 'natural' materials if you can, ie those with the least embodied energy and which can regrow or be resourced locally. • best of all is re-use, restore, extend, improve, recycle, don't demolish if you can help it.